9301375 Chun The purpose of this investigation is to determine the process-structure relationships and the extent of structural control that can be achieved in spray forming with uniform droplets. Unlike gas-atomized spray forming in which structural control is limited by the use of non-uniform droplet sprays and the coupling among the spray process parameters, this research is based on the ability to produce uniform metal droplet sprays with precisely controlled droplet size, thermal state and mass flux. A combination of controlled experiments and analysis may lead o an understanding of how processing variables affect material structure, and may provide knowledge that can be applied to design and control the spray forming process. The experiment include spray forming with controlled droplet solidification, undercooling, mass and enthalpy flux, and with reduced ambient pressure. These experiments are designed to permit studies of the limiting conditions for producing bulk materials with rapidly solidified, novel microstructure directly from the melt. The targeted novel structures are those with fine, uniform, equiaxed grains, controlled texturing and amorphous phases. The uniform droplet spray forming process, including the droplets generation, fluid-thermal state at impact and mass flux as well as the substrate condition, will be characterized and modeled. These results will be compared with the experimental observations on the microstructure evolution to establish process-structure relationships in the spray forming process.
